A large global but decentralized computer network consisting of many subnetworks is generally referred to as the Internet. Such subnetworks can for example be local networks which are geographically restricted. These local networks are also known as Local Area Networks or LANs and can for example be computer networks of individual companies or institutions.
The Internet Protocol, abbreviated to IP, is used for data transfer in the Internet or transfer from or to the individual subnetworks of the Internet. IP is responsible for the connectionless transport of data in packet form—so-called IP packets—from a computer in a subnetwork to a target computer in a subnetwork via a number of subnetworks. So that an IP data packet can be directed to a specific computer in a subnetwork, addressing of the computers in the subnetworks is undertaken in IP. Each computer is assigned an address which is valid in the Internet, known as its IP address, when it is set up.
The communication process will be further explained with the aid of the OSI reference model, which appears especially useful for describing this process. The OSI reference model comprises 7 layers, with                the first layer defining protocols which operate directly on the medium,        the second layer transferring data which is exchanged between two stations, with an error-detection and/or correction protocol,        the third layer handles the transmission of data packets,        the fourth layer looks after the end-to-end connection,        the main task of the fifth layer is the acceptance, the basic execution and the ending of a session from the application layer (also known as layer 7),        the sixth layer interprets the data and ensures the correct syntax and        the seventh layer makes directly distributed data transmission applications available to the user and his programs.        
In accordance with the OSI reference model the addressing of a computer is now assigned by the layer 3 IP address. The IP address allows unique addressing of a computer in the Internet or in the subnetwork to which it is assigned. This means that a data packet can be transmitted on the basis of this address valid in the Internet from a sending computer to a target computer, with the two computers being in different subnetworks. The forwarding of the data packets between the subnetworks is undertaken using the IP address. In this case, in accordance with the OSI reference mode data packets received from layer 2 of the OSI reference model which is also called the link layer are transferred, in layer 3, which is also referred to as the network layer. The decision is then made in layer 3 on the basis of the IP address as to the destination of the data packets. In addition to forwarding data packets between various subnetworks, monitoring of the network utilization is also a task of layer 3 of the OSI reference model, which is why the option of buffering data packets is provided in this layer.
Within a subnetwork, especially when this is implemented as a LAN, an additional addressing of the individual computers in the local network is undertaken in layer 2 of the OSI reference model. Layer 2 of the OSI reference model provides an error-free connection between computers as a service within a network. In addition layer 2 also undertakes flow control if data packets cannot be transmitted as quickly as they are being transferred from layer 3 of the OSI reference model. For this flow control a so-called buffer for data packets is provided by layer 2, with a memory of small size for intermediate storage of data packets being referred to as a buffer.
In a LAN, In accordance with the various layers of the OSI reference model, a distinction is made between a hardware address, the so-called Media Access Control or MAC address and the IP address valid in the Internet. Each computer in a local network thus has at least one MAC address and one IP address via which it can be accessed and which are known to the computer. The MAC address, which is unique worldwide if the LAN is based on what is known as Ethernet technology, is used for the transmission of data packets within a local network from a sending computer to a target computer.
In Ethernet technology the data is transported over a shared transmission channel. Access to this transmission channel is undertaken using the collision detection method. This means that each computer which has data to send accesses the shared transmission channel when this channel has been identified by the sending computer as free. The collision-detection method detects and indicates simultaneous access by two computers to the transmission channel. The send process is repeated by the computers after a predetermined time. The data is transmitted in Ethernet technology in what are known as datagrams or frames, of which the length is flexible and into which in frame format the address of the target computer and the address of the sending computer within the local network—i.e. the MAC addresses of the computers are entered.
If a data packet in which the address of the target computer is also packed as an IP address is to be directed to the target computer in a subnetwork realized as a LAN, for the transmission of the data packet the IP address of the target computer must be assigned an address of the target computer which is valid in the local network. For an Ethernet technology-based LAN for example the data packet is packed for transmission into a frame and the MAC address of the target computer is entered into this frame. On the basis of this address valid in the local network the data packet is sent to the target computer.
The address valid in the local network belonging to the IP address of the target computer is requested by the computer which forwards the data packet using a protocol such as the Address Resolution Protocol for example. The Address Resolution Protocol, also abbreviated to ARP, has the task of establishing the formats in which computer addresses are present and of converting these if necessary from one format into the other format.
So that the associated network does not have to be determined for each data packet which is sent to a specific target computer and a local network, the assignments of the computer address valid in the Internet and the local network are stored in an address table. The address assignments in this address table are mostly provided with a timer by which their validity is limited. This means that the address assignments are deleted from the address table after a specific time which is determined by the validity timer timing out. If a further data packet is to be sent to the target computer thereafter for which the address assignment has been deleted from the address table, the assignment between the address of the target computer valid in the Internet and the address valid in the local network must be determined once again and stored once more in the address table.
During the renewed determination of the address assignment however no data packets can be sent to this target computer. A transmission of data packets can only be undertaken after the address assignment has been entered into the address table. With the method known from the prior art data packets which are to be sent during the determination and storage of the address assignment for a target computer are stored for this target computer in the buffer in layer 2 of the OSI reference model.